Pakistan's cricketer-turned-politician Imran Khan addresses his supporters on August 15, 2014 in Wazirabad, Pakistan.
Pakistan's Imran Khan vowed on Saturday that thousands of protesters rallying in Islamabad would not move until Prime Minister Nawaz Sharif stepped down, as the cricketer-turned-politician attempts to topple the government he claims was elected fraudulently.
Addressing a rally after leading protesters from the eastern city of Lahore, Mr Khan said he would stage a sit-in on Saturday afternoon that would continue until Mr Sharif leaves office.
"The time has arrived when the nation should decide. I will stay here until the prime minister resigns. We don't accept a prime minister who has been appointed after rigged elections," Khan told supporters in the early hours of Saturday after arriving in the capital.
The May 2013 general election saw Mr Sharif take power in a landslide, and international observers who monitored the polls said they were free and credible.
The demonstration is the culmination of the "long march" -- in reality a motorised cavalcade that set off on Thursday from Lahore, situated around 300 kilometres (190 miles) away, to try to topple the government.
Mr Khan has announced that he will speak again to the gathering at 3:00 pm (1000 GMT), though a delay of several hours would not be uncommon in Pakistan.
The marchers took more than 36 hours to reach the capital as convoys made stopovers in various cities along the road, where they were warmly welcomed.
"We went to the election commission and the supreme court against the rigging in the elections. When we could not get justice, then we decided that there is no other way but to come on roads to get justice," Mr Khan said.
Populist cleric Tahir-ul-Qadri, who led thousands of his own followers alongside Khan, said he would present a list of reforms later in the afternoon he wanted to see enacted, speaking atop a shipping container being used as a stage.
"I will announce my Charter of Demands and Charter of Reforms at 4:00 pm (1100 GMT) today," Mr Qadri said.
Police and witnesses said on Friday that activists from Khan's Pakistan Tehreek-e-Insaaf (PTI) party clashed with supporters of Sharif's Pakistan Muslim League-N (PML-N) in the town of Gujranwala, some 200 kilometres southeast of Islamabad.
Khan said shots were fired on his march, telling ARY television news: "They threw stones at us. They fired bullets at us."
However, police said there were no shots and an AFP photographer at the scene also heard no gunfire.
Supporters of PTI, which came third in last year's election, lined up to welcome the convoy in towns along the Grand Trunk Road that links Lahore and Islamabad.
Exact numbers for the march have not been confirmed and organisers said they expected a clearer picture once all of those who joined the rally congregate in Islamabad.
Slow progress
Both Mr Khan and Mr Qadri had originally planned for their marches to converge on Islamabad on Thursday, Pakistan's independence day, but they made slow progress.
By Friday evening Mr Khan's march was slowed to a snail's pace by PTI well-wishers.
Security in Islamabad has been ramped up in recent days, with more than 20,000 police and security forces on the streets.
The government has agreed to allow the two groups to hold rallies but many of the city's streets are blocked off with shipping containers to protect sensitive areas.
Around 5,000-7,000 PTI supporters, mostly from northwestern Khyber Pakhtunkhwa province, gathered in the capital in preparation for the arrival of the march.
There was a festive mood, with many dancing, singing and waving party flags, despite a torrential monsoon downpour.
'Effort to derail democracy'
Government officials have accused march organisers of trying to derail democracy and Sharif said the marches were a distraction from more pressing issues.
Marvi Memon, a PML-N member of parliament and spokeswoman, said Khan had ignored constitutional routes to address his grievances, including an offer by Sharif to set up a judicial commission to investigate rigging allegations.
"All his efforts are undemocratic and unconstitutional and an effort to derail democracy," she said.
Pakistan is waging a military offensive against Taliban hideouts in the northwest, while also trying to boost a sagging economy and solve a chronic power supply crisis.
Highlighting the fragile security situation facing the nuclear-armed state, militants attacked two airbases in the southwestern city of Quetta on Thursday, with 12 attackers killed by security forces.